I had no idea that I had asthma or that it caused fatigue. I thought asthma meant acute attacks and didn't know that it could also be a chronic condition resulting in perpetual oxygen deprivation. I also didn't know it was aggravated by exercise so I'd get into a cycle where I'd begin exercising regularly and then find that the harder I worked, the less effective I was being. I'd get weaker instead of stronger and it would become less and less fun. Eventually I'd quit, then feel guilty for not having willpower. I thought maybe it was the result of age or that I was depressed. Finally, I went to a doctor who told me my lungs were operating at 50% capacity. I started using an inhaler, and steroids and it helped a lot. I was less tire and could enjoy my African dance classes and hiking again. I slept much better at night and didn't drag through the day. Also, I got weekly allergy shots which made a huge difference. Now the asthma has returned but not as bad. Time to get the allergies reevaluated again. Probably need to start the shots. Also steroids. Sigh. But it really helps.
I used to go to Curves and I would notice that my strength on the machines would shoot up but then start dropping, and that as my strength dropped, so did my enjoyment of the activity. It was really startling. I thought it was adrenal failure too, so yes, go to your doctor for sure!